1. Field of the Invention
The invention relates to an aperture for an electron beam system for pattern writing, and especially to an aperture with cell projecting blocks of an electron beam system with pattern writing capability used in a manufacturing process of a large scale integrated circuit.
2. Brief Description of the Related Art
Because of recent the tendency towards microfabrications and high density integrations in large scale integrated circuits, electron beam lithography, being capable of minute processing, has come to be widely used. In an electron beam system designed for this purpose, an electron beam, being irradiated from an electron source, passes through an aperture, and is shaped into a narrow beam and projected (written) on an electron-beam-sensitive film (resist film) on a semiconductor substrate. The aperture is provided with various kinds of patterns, and the cross-section of the transmitted electron beam through the aperture has a shape suitable for pattern writing. In most cases, patterns to be written on the resist film are repetitive in nature, and the following is regarded as most promising one of increasing the through-put of the electron beam lithography and the flexibility of system operation. That is to say, the cell pattern is cut through the mask as one block, and written on the resist film by the electron beam irradiation at one time. The pattern writing process is continued by scanning the electron beam over the resist film on the substrate.
With regard to the aperture with cell projecting blocks, however, the following disadvantages have been discovered. In constructing a cell projecting block, it becomes sometimes necessary to support plural isolated patterns in a window-like opening, without undesirable shadows of supporting members projected on the resist film. Various methods have been proposed to accomplish this however, heretofore an acceptable method for accomplishing same has not yet been established. Moreover, there are two (positive and negative) types of resist films. Thus, it would be described for the electron beam system to be able to be used with both types of resist films, however, an the electron beam system with such capability has not yet been developed. It should be noted that the aperture is consisted of many aperture portions with cell projecting blocks, and will be discussed in connection with the construction and function of each aperture portion.